The present invention concerns an electrical socket contact with a box-shaped base part with four side walls and a rear connection part for the reception of a conductor wire. Such socket contacts also possess at least two spring arms which are integrated on the side walls in the base part and are arranged opposite and bent towards one another via parts of their lengths and bent back at their flee ends.
Such socket contacts are normally stamped from metal sheet and brought to their ultimate shape, which keeps the cost of manufacture of such socket contacts low. U.S. Pat. No. 4,834,681 discloses an electrical contact which in order to receive an electrical contact pin, possesses two spring arms arranged opposite one another which form the contact part.
EP-B1-0 189 821 discloses a double-faced electrical spring contact which possesses a central box-shaped spring base part with a ceiling pail, two side walls and a floor part. Furthermore, two pairs of spring arms are provided, which are integrated on the floor and the ceiling parts.
Such socket contacts have the drawback that when a contact pin of a complementary plug is introduced, the contact pin is only centred and guided by the two opposed spring arms. A guidance on both sides vertically to the spring arms can take place via an optional box spring, but in this case the axial clearance is greater and the degree of static definition as against the newly described principle of contact is accordingly smaller. This can, in the case of oscillations, vibrations or similar stresses, lead to an increased tendency of the socket system towards fretting corrosion, especially with contact surfaces which are of a base metal such as tin. The consequence is a strong rise of the contact resistance, up to a complete failure of the connector system.
It is the purpose of the invention to provide a better guidance, both of the contact pin of a complementary plug during the introduction into the socket contact (reduction of the degree of freedom) as well as of the box spring in relation to the contact base (reduction of the tendency to tip), whilst retaining a relatively soft spring characteristic which makes it possible to insert various thickness pins, ideally 0.6 mm and 0.8 mm with either a base metal or a noble metal coating.
This purpose is performed by an electrical socket contact which has a guide rail offset with respect to the spring arms and integrated on the periphery of the base part and whose free end extends in the direction of the free end of the contact spring arm, making it possible during the introduction of a counterplug to guide the contact pin not only on both sides of the spring arms, but also, on one side, vertically to the same. This leads to a reduction of the degree of freedom of the pin which has been introduced and thereby also to a reduction of the tendency towards the fretting corrosion.
Preferably, the socket contact is formed form a steel sheet blank so that the manufacture can be carried out simply and cheaply.
The guide rail can be introduced in one or in two parts, where the two halves of the guide rail can be separated from one another by a slot. If the socket contact is made from a steel sheet blank, the guide rail can either be in one part in which case it can be arranged vertically to the plug axis of the socket contact, or, in the case of a two-part guide rail, vertically to the plug axis of the socket contact at both outer ends of the steel sheet blank. In the latter case, the parts of the two-part guide rail lie, after shaping by bending, flush against one another. The two spring arms of the socket contact are preferably slotted, where the slots cannot extend as far as the junction of the spring arms part and the basis part.
The spring arms can be so shaped that, depending on an increasing spring stretch of the base contact, they may alter the support point of the spring arms of the contact base on the inner face of an optional box spring. With an increasing spring path, the support point may wander in the direction of the insertion opening which in turn leads to an increase in the perpendicular contact force.
Furthermore, an extension can be present on the side of the socket contact, lying opposite the guide rail, namely, a second guide rail, whose free end extends against the direction of insertion and lies approximately opposite the free end of the guide rail. This improves further the centering of the contact pin so that an insertion of the contact pin at an angle, that is to say, not parallel to the plug axis, is almost completely prevented.
The box spring can be inserted on the socket contact, whereby the box spring, the guide rail and the spring contact arms form a closed rotating sleeve.
The socket contact can be better protected from external influences and an exact, largely backlash-free fixing of the box spring on the contact base is achieved.
The box spring may have two links bent inwards, whose free ends surround the ends of the spring arms of the contact base. Depending on the spring arms of the contact base and the internal dimensions of the two links, it is possible, during the fitting of the box spring on the contact base, to hold the spring arms in such a way that a slit forms between the said spring arms.